Incandescence

«That's not what I'm talking about,» Zak said patiently. «You moved at a walking pace to a new location, you didn't race the wind. The wind feels something extra, everywhere, compared to the fixed weights on the map, simply because it's in motion, not because those fixed weights change from place to place.»

If this was true it had the potential to resolve the paradox, but the idea still struck Roi as very strange. «Why should it feel something extra just because it's moving?»

«Because the Splinter is spinning,» Zak said. «Now, I know the map already takes account of that, in part. An object fixed to the Splinter is really turning in a circle — a small one, much smaller than its orbit — which frustrates its natural motion and contributes to its weight. There's one further twist, though. Imagine a stone that's moving in a straight line, as seen from outside the Splinter. Because the Splinter is constantly turning, as the stone moves, we're moving too. If we try to trace the path of the stone against our surroundings — against the rocks and tunnels we think of as fixed, but which in truth are turning — the line we see it following won't be a straight line, because of the way our motion adds to the stone's. Its path will seem bent, as if there were a weight constantly pushing it sideways. And the faster the stone moves, the greater the apparent weight bending its path.»

«The faster it moves in reality, or the faster we think it's moving?»

«The faster we think it's moving.»

Roi struggled to visualize it. If a stone moved in a straight line away from the axis of spin, then the rotation of the Splinter would make it seem to follow a spiral path, forever turning. And if the stone was sitting completely still? Then the motion of the Splinter meant that it would appear to be moving in a circle, again with its path constantly veering sideways.

«I think I understand,» she said. «But the wind doesn't wrap itself into a spiral. On the garmside, it blows straight from sharq to rarb.»

Zak said nothing.

Roi struck her carapace. «Of course, that's the whole point! I've been wondering why the weights from the map don't push the wind garmwards, in some kind of curve plunging back out into the Incandescence. But the extra weight from its motion must push it in the other direction, balancing the ordinary weight exactly.»

«That's right,» Zak said. «The further garm you go, the stronger the garmwards weight, but because the wind is also blowing more strongly, the weight from its motion keeps perfect step, and the two of them always cancel.»

Roi was pleased that she'd finally grasped what she'd been missing, but there was still something frustrating about the whole matter. The Splinter was turning, Zak claimed, and this claim turned out to be absolutely vital in order to make sense of the rest of his vision. Without the strange distortions in weight and motion brought about by the spin, it would have been impossible to reconcile a simple concept such as circular orbits for the wind with the ordinary realities of the Splinter.

However, everything about the Splinter's rotation seemed to involve a kind of conspiracy of self-effacement. It contributed to the garm-sard weights on the map, but who was to say exactly how much it added? It balanced a hypothetical rarb-sharq weight exactly, but that perfect balance left nothing behind to be felt or measured. And now it conspired with the garm-sard weights again. in order not to bend the wind.

Roi understood that at least some of this was a logical necessity, not a matter of coincidence. The two points of view, one tied to the rock of the Splinter, the other taking a grand cosmic perspective, were describing exactly the same reality, so of course they had to agree with each other, once you knew how to translate between them. Nonetheless, she couldn't accept that the fact of the Splinter's rotation could be both crucial and completely invisible, impalpable, and immeasurable.

She said, «When I throw a stone in the Null Chamber, why can't I see its path being bent?»

«It's a subtle effect,» Zak said. «I've made some crude measurements of it, but it's hard to detect just by looking.»

«You've measured the Splinter's rotation!» Roi was astonished. «Why didn't you tell me that before?»

«I wouldn't say I'd measured the rotation. My measurements show that the rotation exists, but I haven't come close to quantifying the rate of spin.»

«But you've seen the effect itself?»

«Absolutely,» Zak said.

«Can you show me?»

They went to the Null Chamber, and Zak fished out a device he called a spring-shot from one of the storage clefts. It was a tube fitted with a spring-loaded plunger that could be cocked to varying degrees of compression and then released, propelling a stone from the tube. The projectile emerged in a reasonably predictable direction, with a choice of velocities.